The invention lies in the field of electron optics, ion optics, and particle beam deflection, particularly as it is used in oscilloscopes, scanning microscopes, data storage devices, and ion-beam and electron-beam microfabrication.
In the prior art are found the parallel plate deflector and the magnetic deflector, which exert electric or magnetic forces in a sideways direction on the particles of a beam; the parabola spectrograph of Aston in which, essentially, the north and south poles of an electromagnet are simultaneously made parallel electrodes; and the Wien velocity filter, in which collinear electric and magnetic forces are used to select particles of a narrow band of velocities from a beam having a continuum of velocities.
The prior art also teaches how to focus particle beams by means of quadrupole lenses, which may be solely electric or solely magnetic. Solely magnetic quadrupole lenses which do not incorporate ferromagnetic materials are described in U.S. Pat. No. 2,919,381 of Glaser. The prior art, for instance as summarized in abandoned application Ser. No. 024,707, filed Mar. 28, 1979 of F. W. Martin, also teaches how magnetic and electric quadrupole lenses may be combined to produce achromatic focusing.